Security alarms are almost common items on homes, businesses, and motor vehicles in today's society. Their use has not only stopped many attempted thefts in progress, but the knowledge that they are there, has stopped many more before they are even started. However, there still remain many targets which are a favorite with thieves. One (1) of these targets is the unoccupied semi-trailer rig. It is common knowledge that most of these units do not have a power source to operate an alarm, much less a phone line that connects to a central office. These facts, coupled with their often remote location, unoccupied status, and valuable items and materials contained within, typically lead to a high percentage of thefts. In a matter of minutes, someone can simply drive up with a truck, hitch up, and drive off.
It can be difficult to add measures to prevent theft of the trailers and the contents stored inside. Even when the cargo is secured and locked, once a thief transports the trailer to another location, they are free to brake through any locks provided on the trailer. Theft of cargo in the trucking industry has risen to between $10 to $15 billion annually, and including indirect costs the annual total losses is estimated at nearly $60 billion. Due to the fact that semi-trailers are towed and rely on a tractor for power and air supply, many of the common personal vehicle security measure are not available.
Traditionally, trailer operators have used mechanical locking devices which physically prevent attachment of the trailer to a tractor or other tow vehicle. However, these devices are easily defeated and require the operator to remember to manually set the lock in order to be effective.
The trailer utilizes a spring-biased parking and emergency brake systems which require a supply of compressed air to disengage the spring brakes. The spring brake system is configured so the spring brake units are engaged by a spring force to lock the brake cylinder in response to a low pressure condition in the air brake air line and release the brakes in response to a high pressure condition when the supply of compressed air is attached. The tractor or other tow vehicle used for hauling the trailer has an air compressor that provides the supply of compressed air to the trailer through a service and emergency brake air line. The operator disconnects the brake air lines when the trailer is released from the tractor and the lines are purged to biases the spring brake to lock the wheels to prevent movement of the trailer. Since semi-trailers rely on the compressed air provided by the tractor to operate the braking systems, various theft deterrent devices have been attempted by utilizing the air brakes to prevent movement.
While many of these attempts may achieve their purported objectives, they suffer from various disadvantages and deficiencies related to design or utilization. Particularly, these devices can be costly and complicated to install and implement and utilize a variety of sensors in order to operate correctly. Additionally, failure of these devices can lead to accidental engagement of the spring brake units while the trailer is moving which can lead to disastrous accidents.